Static mixer and method of making same

ABSTRACT

A static mixer and method of making the same which mixer is capable of simultaneously mixing together a plurality of fluids, usually at least two liquids, in a stream which may be segmented by a fluid which may be a gas, comprising one or more elements forming an elongated fluid passageway for conveying the fluids while at least two liquids are intermixed. A helix is formed within the passageway to impart a rotational movement to the stream so that the rotational velocity at the liquid-wall interface is greater than that at the center of the stream, providing an efficient mixing action, without breaking up the gas segments.

Elite Sgg Dannewitz et all.-

[54] STATE: MIXER AND METHOD OF MAKING SAME [72] inventors: Robert E. Dannewitz, Yonkers, N.Y.; Al-

hert M. Luongo, Emerson, NJ.

[73] Assignee: Technicon Instruments Corporation, Tarrytown, NY.

[22] Filed: Aug. 3, 1970 [21] Appl. No.: 60,474

Harder ..259/4 Stearns ..259/4 Heyl ..259/4 Primary Examiner-Robert W. Jenkins Attorney-S. E. Rockwell [5 7] STRACT A static mixer and method of making the same which mixer is capable of simultaneously mixing together a plurality of fluids, usually at least two liquids, in a stream which may be segmented by a fluid which may be a gas, comprising one or more elements forming an elongated fluid passageway for conveying the fluids while at least two liquids are intermixed. A helix is formed within the passageway to impart a rotational movement to the stream so that the rotational velocity at the liquidwall interface is greater than that at the center of the stream, providing an efiicient mixing action, without breaking up the gas segments.

7 Claims, 5 Dra Figures PATENTEUMAR 71912 3.647, 187

IN VIiN'l 0R5 ROBERT E. DANNEWITZ ALBERT M. LUONGO ATTORNEY STATIC MIXER AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to static mixers of the helical type, useful in continuous-flow analysis apparatus of the automated kind.

2. Prior Art l-leretofore, in automated continuous-flow analysis apparatus such as that illustrated and described in U.S. Pat. No. 2,797,149 issued June 25, 1957 and in U.S. Pat. No. 3,241,432 issued Mar. 22, 1966, it has been common to intermix a liquid sample with a reagent or a diluent in a stream segmented by a fluid, usually a gas, in a coil (formed of a length of helically shaped tubing of glass, plastic or other suitable material) by a gravitational action. When such a mixer is employed for gravitational mixing in which one liquid part is of greater density than another in the same segment, the axis of the helix or coil should be arranged horizontally so that each liquid segment tends to be inverted as it passes up, over and under the last-mentioned axis moving through the turns of the coil. However, in such automated apparatus, it is not uncommon in mixing liquids generally to arrange the coil vertically, because of space limitations or other considerations, though the mixing action is believed to be inferior. These mixing coils may, and usually do, have turns of equal diameter forming the fluid passageway. Also, mixers of this type have been employed to suspend or wash particulate matter in a liquid.

In dialysis modules employed in such automated analysis apparatus it has been common to provide an elongated liquid passageway in both the donor and recipient streams in an attempt to provide greater exchange between the streams, one of which is superimposed on the other and separated by a membrane. The long passageway has taken the form of a flat or pancake spiral. In some dialysis units certain factors have dictated a shortened, straight passageway for each of these companion streams.

In a dialyzer, as in other liquid-conveying passages, stagnation of liquid is likely to occur at the liquid-wall interface. Dialysis occurs across the membrane until equilibrium is achieved. This equilibrium may be reached fairly slowly in stagnant regions. It is therefore desirable to mix each of the donor and recipient streams flowing along the membrane, but particularly the recipient stream, to present fresh liquid to the membrane or, in other words, to tend to expose all parts of the liquid to the membrane for a better exchange between the donor and recipient streams.

At least in certain applications, the aforementioned coil mixer has proven inefi'rcient in use. Also, the length of the passageway formed by such a mixer may be a drawback. As indicated dialysis is retarded by stagnant zones of liquid lying along a dialysis membrane which zones may be eliminated by proper liquid mixing.

Static mixers of the restrictive type have found some acceptance but have not been effective as mixers in many applications. U.S. Pat. No. 3,286,992 issued Nov. 22, 1966 discloses a static mixer which is not of the restrictive type and also not of the coil type. While it is of the helical type, it is a complicated structure comprising many bafflelike elements. Moreover, it would not convey a gas-segmented sample stream without breaking up the gas segments which maintain sample integrity and isolation. Its use would mix samples together.

SUMMARY OF THE INVENTION One object of the invention is to provide an improved static mixer of the helical type which may be used in automated continuous-flow analysis of liquid samples which are conveyed seriatum in a gas-segmented stream, in which the samples are mixed with a color producing reagent and/or another liquid, prior to examination as in a colorimeter for example.

According to the invention, the mixer is not restricted to mixing a sample with a reagent or diluent or both but may be utilized in a dialyzer, for example, where it is desired to avoid stagnation of a part or parts of a liquid stream by imparting a rotational movement to the peripheral portion of the stream.

There is provided a mixer structure having a fluid passageway therein in which lies either a male or female helix to impart a rotational spin to the liquid in the passageway, setting up currents in the liquid which tend to have an effective mixing action.

The mixer in a simple form may be structured by one or more elements which provide an elongated bore of uniform cross section and a light helical spring in the bore lying along and against the wall structure thereof to impart a rotational movement to fluid flowing in the bore. On the other hand, it may be formed in one piece of metal, glass, plastic or ceramic material, structured as a tube with a male or female thread in the bore thereof. It may be manufactured by a simple molding, pressing or twisting operation, for example, or by shrinking over a core. The tube in its final shape may be as long or short as desired and may be straight or have bends in it so as to form a variety of shapes such as an L or an S. It may be horizontally or vertically arranged and still provide an efficient mixing action. It also may be mounted with conventional end fittings.

Besides its effective mixing action and simplicity of construction, the mixer has the advantage of passing or conveying a liquid stream segmented by a fluid such as air bubbles, for example, as used in analysis apparatus such as that shown and described in U.S. Pat. No. 3,334,018, issued Aug. l, 1967, without breaking the air bubble pattern. Air bubbles are commonly used to separate one segment of a sample-reagent stream from another to maintain sample isolation and integrity and to cleanse the tubing wall to reduce contamination of one sample from another. These segmenting air bubbles are of a size to extend across the internal diameter of the mixer passageway, and the bubbles have a tendency to rotate in the passageway much as a bullet spins on its axis in a rifled bore.

The mixer may be utilized to mix a variety of fluids such as blood or components thereof with various reagents or diluents. It may be used to mix fluids which are other than body fluids, as in apparatus for monitoring industrial operations or air pollution.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a fragmentary, longitudinal elevational view in section illustrating a dialyzer incorporating a static mixer embodying the invention;

FIG. 1A is an elevational sectional view of the dialyzer taken at a right angle with reference to FIG. 1;

FIG. 2 is a fragmentary, longitudinal sectional view illustrating a modified form of the invention as applied to a tubular structure;

FIG. 3 is a fragmentary view of a core member which may serve as a mold element to form another embodiment of the invention in a tubular structure; and

FIG. 3A is a fragmentary, sectional view illustrating the modified form of mixer which may be made with the use of the core member of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and IA there is shown a dialyzer indicated generally at 10 comprising upper and lower dialyzer plates which may be formed of metal, indicated respectively at 11 and 12. The upper plate 11 has an elongated downwardly facing channel 13 therein, and the lower plate 12 has an upwardly facing complemental channel 14 formed therein registering with the channel 13 when the plates 11 and 12 are assembled as shown in FIG. IA. Each of the illustrated channels l3, 14, may be of a cross section such as illustrated, having a rounded bottom formed on a radius. This avoids sharp corners in which particulate matter, for example, might be trapped. The rounded bottom of the channel 14 serves another function which will appear hereinafter.

Between the dialyzer plates 11 and 12 and sandwiched thereby. lies a dialyzing membrane in the form of a sheet which may be formed of any efficient dialyzing material such as cellulose, for example. The membrane, indicated as 15, separates the channels 13 and 14. Within the channel 14 of the lower plate, which may receive the recipient stream, and preferably extending from end to end is a light helical spring 16 which defines a helical thread. The spring 16 may be relaxed, that is, the spring need not be compressed nor tensioned in the channe The cross section of the spring 16 extends between the sides of the channel 14 as shown in FIG. 1A and is of a diameter approximating the depth of the channel 14. The illustrated arrangement is such that the spring contacts the membrane 15, and the membrane may be slightly deformed thereby as shown. This deformation extends along the interrupted lines of contact of the spring with the membrane throughout the length of the fonner. As shown, the radius of the spring 16 is complemental to the radius of the bottom of the channel 14, and the spring fits thereagainst. The dialyzer plates are provided with attachment flanges as shown in FIG. 1A which receive fasteners 17 by which the upper and lower dialyzer plates 11 and 12 may be secured together in clamping relation to the membrane 15.

In the form illustrated by way of example, the donor stream of the dialyzer may flow through the channel 13 in the upper dialyzer plate. The spring 16 imparts a rotational movement to the liquid passing through the lower channel 14, the peripheral portion of this stream tending to flow at a faster velocity. This action, which creates currents in the lower stream, provides good mixing of .the liquid in the channel 14 and exposure of substantially all parts of the liquid to the membrane 15, thereby effectively tending to avoid any stagnant regions lying along the underside of the membrane 15. In

other words, the fluid exchange at this side of the membrane is enhanced. It is common to transmit liquid through the dialyzer fluid passageways by the action of a pump as indicated in US. Pat. No. 2,797,149, supra. In view of the disclosure in the last mentioned patent it is unnecessary here to further describe the details of the dialyzer.

If desired, the spring 16 may be placed in the bore 13 of the dialyzer instead of the bore 14, or similar springs may be employed in both bores instead of one. A further alternative construction resides, instead of the use of one or more springs, in the provision of angular cuts or molded projections on the rounded bottom of one or both dialyzer channels to impart a rotational movement to the gas-segmented liquid moving therethrough.

In none of these constructions are gas segments or bubbles separating liquid segments lost in the sense of destruction of the bubble pattern, which bubbles are of a size to extend across the respective channel. The angular surface portions of the respective fluid passageway tend to impart a rotational spin to the bubbles. It will be appreciated from the foregoing that both the donor and recipient streams may be segmented by inert bubbles of gas such as air.

In the modified form of FIG. 2, the invention is shown embodied'in a tube of glass of suitable plastic material. A tube of appropriate length for the mixer and having an appropriate wall thickness and inner diameter is provided into which a helical spring, not shown, is inserted. The spring, which may be longer than the tube, is of a diameter approximately as large as the tube bore and, if desired, may be somewhat compressed when inserted in the tube.

mately 0.01 to 0.2 inch.

The resultant tubular structure is that shown in FIG. 2 wherein the tube is indicated generally at 18, having a female helix or thread 19 on its inner surface the pitch of which may be within the range of fifty to one per inch by way of example. The invention is well suited to the forming of mixer tubing have relatively small inner diameters in the range of approxi- In the form of FIG. 2, it will be noted that the outer surface 20 of the tube 18 as well as the inner surface 21- has been deformed from its original condition to a shape in which it has a spiral peak 22 and a depression 23 units outer surface 20'. The peak 22 and depression 23 correspond with a spiral depression 24 and peak 25, respectively, on the inner tube surface 21. The spiral peak 25 may have a gentle slope, more so than the depression 24, as shown in FIG. 2. As will appearhereinafter the wall portion of the tube may be essentially flat between inner deformed portions of the tube, unlike the wall surface 25.

Either end of the tube .18 may be the inlet end of the mixer and the other end the outlet, each end cooperating with a sleeve coupling element, not shown, for mounting purposes.

Rotational movement is imparted to the stream flowing through the mixer, the streamusually being pushed or pulled by a pump. As previously indicated the stream may be subjected to the action of the mixer for suspending particulate matter in a liquid. The mixer may also be used to wash or scrub particulate matter in a liquid.

The stream on which the mixer works may contain a series of liquid samples, each different from another, for analysis. Air or other inert gas bubbles separate the samples to maintain sample integrity and cleanse the wall of the tubing, the sample segments each including a previously added quantity of a reagent or diluent or both, the contents of which segments require mixing prior to sample examination as in a colorimeter for example.

The gas bubbles or segments in such a stream extend across the diameter of the helical mixer and do not lose their identity or above-described function as they move through the mixer. They are not broken up by the helical wall surface of the mixer, and their liquid-segmenting pattern is retained as they pass through the mixer. The bubbles have a tendency to rotate while passing through the mixer. Due to the mixer construction, the rotationalvelocity of the liquid at the liquid-wall interface is greater than that at the center of the stream, providing currents which effect an efficient mixing action. Bubbles passing through the mixer may have a configuration similar to that of the bubble shown in FIG. 2 in phantom and indicated at 26, at the particular axial position illustrated. It will be understood that the bubble configuration alters as. it passes through the mixer;

While it has been stated that samples to be mixed are separated in the mixer by fluid segments comprising a gas, it is to be understood that the samples may be separated by a fluid other than a gas or by a plurality of fluids. US. Pat. No. 3,047,367 granted July 31, 1962 shows and describes one such alternative in automatic analysis with fluid segmentation, wherein the segmenting fluid is an inert immiscible liquid.

A core member such as that shown in FIG. 3 and indicated generally at 27 may be employed to structure the helical static mixer of the form shown in FIG. 3A and indicated generally at 29. The mixer 29 functions in a manner similar to the mixer 18 described above. It is shown by way of example only, and may be constituted by a length of plastic tubing material sold under the trademark Teflon and having a shrinking characteristic on exposure to heat. The core member 27 may have a The tube is then heated by any suitable means until it softens sufficiently for thespring to deform at least the inner, previously uniform, surface of the tube so that it conforms to the helix throughout the area of contact with the spring. The

product is then cooled until the tube material hardens, and

then the spring is removed by rotating it from one end in a direction to decrease the diameter of its turns, or it is merely pulled out of one end of the tube.

cylindrical surface 31 thereof. This groove may be cut as shown so as to have a V-shape in cross section, the angle of which may be approximately 120. If desired the cross section of the groove may be formed on a radius.

The static mixer resulting from the use of the particular core member 29 has the configuration shown in FIG. 3A. On shrinking as aforesaid, the tubing wall conforms to the grooved surface of the core member 27. After the material cools and hardens, the core member may be removed by threading it out of the tube.

The product of such a molding operation has a tubular shape provided with an inner surface 32 having a male helix or thread formed therein. This particular configuration has internally a relatively sharp spiral peak 33 and an intervening essentially flat wall surface portion 34. Here, again, the outer surface of the tube has a helix 35 formed therein.

It will be appreciated that in some forms the mixer of the invention may be bent to desired shapes such as S and L configurations for example. It will also be apparent that the mixer may be formed by other techniques such as twisting, for example, and that it may be formed of other materials such as metal or ceramic material.

it is believed that many advantages of this invention will now be apparent to those skilled in the art. The foregoing description is illustrative, rather than limiting, as a number of variations and modifications may be made without departing from the true spirit and scope of the invention. The invention is limited only by the scope of the following claims.

What is claimed is:

ll. A static mixer for continuous-flow analysis comprising: means defining an elongated fluid conduit having an inlet end and an outlet end, for conveying a liquid stream of unique samples seriatum, the samples being separated by fluid segments, and means extending along at least a portion of the length of said conduit on the inner surface thereof, to impart a rotational movement to at least the outer part of the stream, whereby the contents of each liquid segment are mixed without destruction of the sample-separating fluid segments, the last-mentioned means comprising a helical groove formed in the inner surface of said conduit.

2. A method of making a static mixer comprising: the step of inserting a coil spring within a tube of a material characterized by softening on exposure to heat and hardening when cooled, exposing the assembly to a source of heat until at least the inner wall surface of the tube is deformed by the spring, and allowing the assembly to cool after which the spring is removed from the tube.

3. A method of making a static mixer comprising: providing an elongated core member of generally cylindrical cross section having a helix formed on the outer surface thereof, the step of inserting the core member into a tube of a material characterized by softening and shrinking on exposure to heat and hardening when cooled, exposing the assembly to a source of heat until the tube shrinks and at least the inner wall surface of the tube is deformed to conform to said surface of the core member, and allowing the assembly to cool after which the core member is removed.

4. A static mixer for continuous-flow analysis comprising: means defining an elongated fluid conduit having an inlet end and an outlet end, for conveying a liquid stream of unique samples seriatum, the samples being separated by fluid segments, and means extending along at least a portion of the length of said conduit on the inner surface thereof to impart a rotational movement to at least the outer part of the stream, whereby the contents of each liquid segment are mixed without destruction of the sample-separating fluid segments, said means defining said conduit including a dialysis membrane.

5. A static mixer as defined in claim d, wherein said means for imparting rotational movement to at least the outer part of said stream comprises a helical member of springlike form.

6. A static mixer for continuous-flow analysis comprising:

means defining an elongated fluid conduit having an inlet end and an outlet end, for conveying a liquid stream of unique samples seriatum, the samples being separated by fluid segments, means extending along at least a portion of the length of said conduit on the inner surface thereof, to impart a rotational movement to at least the outer part of the stream, whereby the contents of each liquid segment are. mixed without destruction of the sample-separating fluid segments, said means defining a conduit comprising a tubular member, and said means for imparting rotational movement to at least the outer part of said stream defines a helical thread formed as an integral part of the inner surface of said conduit which thread is of female configuration, and said helical thread effects a relatively gentle depression in said inner conduit surface and a gently sloping peak surface portion on either side of the depression.

7. A static mixer for continuous-flow analysis comprising: means defining an elongated fluid conduit having an inlet end and an outlet end, for conveying a liquid stream of unique samples seriatum, the samples being separated by fluid segments, and means extending along at least a portion of the length of said conduit on the inner surface thereof, to impart a rotational movement to at least the outer part of the stream, whereby the contents of each liquid segment are mixed without destruction of the sample-separating fluid segments, said means defining a conduit comprising a tubular member, and said means for imparting rotational movement to at least the outer part of said stream defines a helical thread formed as an integral part of the inner surface of said conduit which thread is of male configuration, and said helical thread effects a relatively sharp peak in said inner conduit surface and an essentially flat portion on either side of the peak. 

1. A static mixer for continuous-flow analysis comprising: means defining an elongated fluid conduit having an inlet end and an outlet end, for conveying a liquid stream of unique samples seriatum, the samples being separated by fluid segments, and means extending along at least a portion of the length of said conduit on the inner surface thereof, to impart a rotational movement to at least the outer part of the stream, whereby the contents of each liquid segment are mixed without destruction of the sample-separating fluid segments, the last-mentioned means comprising a helical groove formed in the inner surface of said conduit.
 2. A method of making a static mixer comprising: the step of inserting a coil spring within a tube of a material characterized by softening on exposure to heat and hardening when cooled, exposing the assembly to a souRce of heat until at least the inner wall surface of the tube is deformed by the spring, and allowing the assembly to cool after which the spring is removed from the tube.
 3. A method of making a static mixer comprising: providing an elongated core member of generally cylindrical cross section having a helix formed on the outer surface thereof, the step of inserting the core member into a tube of a material characterized by softening and shrinking on exposure to heat and hardening when cooled, exposing the assembly to a source of heat until the tube shrinks and at least the inner wall surface of the tube is deformed to conform to said surface of the core member, and allowing the assembly to cool after which the core member is removed.
 4. A static mixer for continuous-flow analysis comprising: means defining an elongated fluid conduit having an inlet end and an outlet end, for conveying a liquid stream of unique samples seriatum, the samples being separated by fluid segments, and means extending along at least a portion of the length of said conduit on the inner surface thereof to impart a rotational movement to at least the outer part of the stream, whereby the contents of each liquid segment are mixed without destruction of the sample-separating fluid segments, said means defining said conduit including a dialysis membrane.
 5. A static mixer as defined in claim 4, wherein said means for imparting rotational movement to at least the outer part of said stream comprises a helical member of springlike form.
 6. A static mixer for continuous-flow analysis comprising: means defining an elongated fluid conduit having an inlet end and an outlet end, for conveying a liquid stream of unique samples seriatum, the samples being separated by fluid segments, means extending along at least a portion of the length of said conduit on the inner surface thereof, to impart a rotational movement to at least the outer part of the stream, whereby the contents of each liquid segment are mixed without destruction of the sample-separating fluid segments, said means defining a conduit comprising a tubular member, and said means for imparting rotational movement to at least the outer part of said stream defines a helical thread formed as an integral part of the inner surface of said conduit which thread is of female configuration, and said helical thread effects a relatively gentle depression in said inner conduit surface and a gently sloping peak surface portion on either side of the depression.
 7. A static mixer for continuous-flow analysis comprising: means defining an elongated fluid conduit having an inlet end and an outlet end, for conveying a liquid stream of unique samples seriatum, the samples being separated by fluid segments, and means extending along at least a portion of the length of said conduit on the inner surface thereof, to impart a rotational movement to at least the outer part of the stream, whereby the contents of each liquid segment are mixed without destruction of the sample-separating fluid segments, said means defining a conduit comprising a tubular member, and said means for imparting rotational movement to at least the outer part of said stream defines a helical thread formed as an integral part of the inner surface of said conduit which thread is of male configuration, and said helical thread effects a relatively sharp peak in said inner conduit surface and an essentially flat portion on either side of the peak. 